This invention relates to image quality correction devices that carry out a variety of processes on an image signal to correct quality of an image reproduced based on the image signal and, more specifically, to an image quality correction device that corrects the image quality with an appropriate amount of correction according to an amount of jitter in a video signal that greatly affects the image quality.
FIG. 22 is a conventional image correction device used for an analog video signal Sv, based on which an image is displayed on an image display device used in a television set typified by an LCD or CRT. As shown in the drawing, a signal processing system SPc in the television set carries out a variety of processes on the video signal Sv, and generates signals required for displaying images on an image display device 9 (in the present example, CRT), that is, a scan speed modulation signal VSCc, an image signal Si, and a horizontal synchronization signal Hsync, and a vertical synchronization signal Vsync, each carrying information according to the characteristics of the image display device 9.
Based on the scan speed modulation signal VSCc, a scan speed modulation driver 6 carries out scanning at a predetermined speed, and generates an image quality correction scan drive signal Sscd to correct the quality of the image displayed on the image display device 9. Based on the image signal Si, a CRT driver 7 generates a CRT drive signal Scrtd for making the image display device 9 display an image. Based on synchronization signals Ssync, the deflector 8 generates a deflection drive signal Sdfd for making the image display device 9 operate with a predetermined amount of deflection and carry out raster scanning. The image display device 9 is driven by these drive signals Sscd, Scrtd, and Sdfd to display the image carried by the video signal Sv.
The signal processing system SPc includes a sync separator 4, an image quality correction device IQCc, and a signal processor 5. The sync separator 4 extracts the horizontal synchronization signal Hsync and the vertical synchronization signal Vsync from the video signal Sv.
Based on the horizontal synchronization signal Hsync and the vertical synchronization signal Vsync, the image quality correction device IQCc performs image quality correction processing on the video signal Sv, and generates an image-quality-corrected video signal SIQc, and also generates the scan speed modulation signal VSCc. Based on the image-quality corrected video signal SIQc, the signal processor 5 generates the image signal Si. Note that the operation of the signal processing system SPc is controlled by a controller 100c. 
The image quality correction device IQCc includes a scan speed modulation signal generator 11 for defining a scan speed for the image display device 9, a horizontal edge enhancer 12 for defining an amount of horizontal edge enhancement for the image signal Si, a noise reducer (NR) 13 for reducing noise components included in the image signal Si, a multiplexer 14, a bus interface 15, and ROM 16.
Based on the horizontal synchronization signal Hsync, the vertical synchronization signal Vsync, and the video signal Sv, the scan speed modulation signal generator 11 determines a raster scan speed VSC (not shown) that corresponds to the image signal Si. Similarly, based on the horizontal synchronization signal Hsync, the vertical synchronization signal Vsync, and the video signal Sv, the horizontal edge enhancer 12 determines an amount of horizontal edge enhancement OE (not shown) of the video signal Sv.
Even if the video signal Sv is uniform in quality, the video carried by the video signal Sv and displayed on the image display device 9 is affected by physical characteristics of the television set including the image display device 9; a drive circuit system such as the scan speed modulation driver 6, the CRT driver 7, and the deflector 8; and a signal processing system. Therefore, the above-stated scan speed VSC and amount of horizontal edge enhancement OE cannot be uniquely determined based on the horizontal synchronization signal Hsync, the vertical synchronization signal Vsync, and the video signal Sv. For this reason, depending on the physical characteristics of the television set where the image quality correction device IQCc is used, each predetermined amount of correction is calculated in advance for a correcting operation of each of the scan speed modulation signal generator 11, the horizontal edge enhancer 12 and the NR 13.
Then, predetermined amounts of correction SCAc are stored in the ROM 16. When the quality of the image carried by the video signal Sv is corrected by the image quality correction device IQCc, the predetermined amounts of correction SCAc are read from the ROM 16 thorough a bus interface 15, and supplied to the scan speed modulation signal generator 11, the horizontal edge enhancer 12, and the NR 13 for correcting each operation.
Specifically, the predetermined amounts of correction SCAc include a correction amount of scan speed SVMc that is predetermined for the scan speed VSC defined by the scan speed modulation signal generator 11; a correction amount of horizontal edge enhancement SOEc that is predetermined for the amount of horizontal edge enhancement OE defined by the horizontal edge enhancer 12; and a correction amount of noise reduction SNRc that is predetermined for the amount of noise reduction by the NR 13.
As such, the horizontal edge enhancer 12 determines the amount of horizontal edge enhancement OE of the video signal SV based on the correction amount of horizontal edge enhancement SOEc supplied by the ROM 16 via the bus interface 15, and generates a horizontal-edge-enhancement-corrected signal OEc. The multiplexer 14 multiplexes the video signal Sv with the horizontal-edge-enhancement-corrected signal OEc, and generates a horizontal-edge-enhanced-corrected signal VOEc, which is the video signal Sv enhanced in horizontal edge by the amount of horizontal edge enhancement OE.
In a similar manner to that of the horizontal edge enhancer 12, the NR 13 reduces noise of the horizontal-edge-enhanced video signal VOEc, and generates the image-quality-corrected video signal SIQc, based on noise reduction characteristics corrected with the correction amount of noise reduction SNRc supplied by the ROM 16 through the bus interface 15.
The image processor 5 generates the image signal Si based on the image-quality-corrected video signal SIQc.
As described above, in the conventional image quality correction device IQCc, the video signal Sv is corrected in scan speed modulation, horizontal edge amount, and noise reduction for each predetermined amount, considering effects of the physical characteristics of the television set and other factors. In other words, the amount corrected by the image quality correction device IQCc is always constant irrespectively of change in quality of the video signal Sv.
However, the quality of the video signal Sv changes with time. If the video signal Sv jitters, the image-quality-corrected video signal SIQC and scan speed modulation signal VSCc outputted from the image quality correction device IQCc also jitter. Therefore, based on these jittering image-quality-corrected video signal SIQc and the scan speed modulation signal VSCc, the amount of jitter in video reproduced by the video display device 9 is increased, thereby deteriorating the reproduced video in quality.
For example, if the video signal Sv having jitter is subjected to horizontal edge enhancement for greatly enhancing the edge, glare at an edge part is enhanced by jitter in the horizontal edge enhancement signal itself. Thus, the jitter in the reproduced image is enhanced by the image quality correction processing. To prevent this, the amount of image quality correction for edge enhancement is reduced, while the one for noise reduction is increased.
In other words, to prevent video image quality deterioration or to improve video image quality resulting from the quality (jitter) of the video signal Sv, each correction by the scan speed modulation signal generator 11, the horizontal edge enhancer 12, and the NR 13 is adjusted according to the amount of jitter in the video signal Sv. That is, if the video signal Sv jitters, corrections by the scan speed modulation signal generator 11 and the horizontal edge enhancer 12 are suppressed, while the one by the NR 13 is promoted.
For this purpose, the presence or absence of jitter of the video signal Sv and the amount of jitter have to be accurately detected. Conventionally, however, means for accurately detecting the presence or absence of jitter of the input video signal Sv and the amount of jitter is not provided as being incorporated in an image display device such as a television set.
To solve the above problems, a first aspect of the present invention is a jitter detection device for detecting jitter in a video signal, comprising:
a vertical period measuring unit for measuring a vertical period for one field of the video signal and generating a vertical period signal;
a jitter determination unit for determining, based on the vertical period signal, whether the video signal jitters or not, and generating a jitter determination signal;
a jitter determination counter for counting, based on the jitter determination signal, the number of times it is successively determined that the video signal jitters, and generating a jitter determination counter signal;
a jitter confirmation unit for confirming, based on the jitter determination counter signal, that the video signal is a jitter signal if it is determined a first predetermined number of times that the video signal jitters;
a non-jitter counting unit for counting, based on the jitter determination signal, the number of times it is successively determined that the video signal does not jitter, and generating a non-jitter determination counter signal;
a non-jitter confirmation unit for confirming, based on the non-jitter determination counter signal, that the video signal is a non-jitter signal if it is determined a second predetermined number of times that the video signal does not jitter.
As described above, in the first aspect, the state and the jitter amount of the video signal can be accurately detected while eliminating the effects of disturbance factors such as noise components of the video signal or a television set side.
According to a second aspect, in the first aspect, the jitter determination unit:
determines that the video signal jitters when an absolute value of a difference between a vertical period of a present field and a vertical period of a previous field Stf is larger than 1; and
determines that the video signal does not jitter when the absolute value is smaller than 1.
A fourth aspect is directed to an image quality correction device for correcting quality of an image reproduced based on a video signal according to an amount of jitter in the video signal, further including an image quality correction adjuster that comprises at least one of:
a noise reduction unit for reducing noise of the video signal based on a predetermined correction amount of noise reduction;
a horizontal edge enhancer for enhancing a horizontal edge of the video signal based on a predetermined correction amount of horizontal edge enhancement; and
a scan speed modulator for enhancing a specific part of the video signal based on a predetermined amount of scan speed modulation, wherein:
according to the amount of jitter, the correction amount of noise reduction is increased by a predetermined adjustment value, the correction amount of horizontal edge enhancement is decreased by the adjustment value, and the amount of scan speed modulation is decreased by the adjustment value.
As described above, in the fourth aspect, image quality can be corrected with appropriate adjustment according to the state of jitter of the video signal.
According to a fifth aspect, in the fourth aspect, the image quality correction device further comprises a jitter detection device that comprises:
a vertical period measuring unit for measuring a vertical period for one field of the video signal and generating a vertical period signal;
a jitter determination unit for determining, based on the vertical period signal, whether the video signal jitters or not, and generating a jitter determination signal;
a jitter determination counter for counting, based on the jitter determination signal, the number of times it is successively determined that the video signal jitters, and generating a jitter determination counter signal;
a jitter confirmation unit for confirming, based on the jitter determination counter signal, that the video signal is a jitter signal if it is determined a first predetermined number of times that the video signal jitters;
a non-jitter counting unit for counting, based on the jitter determination signal, the number of times it is successively determined that the video signal does not jitter, and generating a non-jitter determination counter signal;
a non-jitter confirmation unit for confirming, based on the non-jitter determination counter signal, that the video signal is a non-jitter signal if it is determined a second predetermined number of times that the video signal does not jitter.
According to a sixth aspect, in the fifth aspect, the image quality correction adjuster dynamically adjusts at least one of the correction amount of noise reduction, the correction amount of horizontal edge enhancement, and the amount of scan speed modulation, while sequentially calculating a dispersion value of vertical periods.
According to a seventh aspect, in the sixth aspect, the image quality correction adjuster further comprises a histogram unit for generating a histogram composed of a frequency of appearance with respect to the amount of jitter, wherein:
at least one of the correction amount of noise reduction, the correction amount of horizontal edge enhancement, and the amount of scan speed modulation is adjusted by an amount of adjustment predetermined corresponding to the amount of jitter and the frequency of appearance that is larger than a predetermined threshold.
According to an eighth aspect, in the fourth aspect, the amount of jitter in a present field is used as the adjustment value immediately after the video signal is changed from a non-jitter signal to a jitter signal.
According to a ninth aspect, in the fifth aspect, the image quality correction device comprises an adjustment suppressor for suspending adjustment of at least one of the correction amount of noise reduction, the correction amount of horizontal edge enhancement, and the amount of scan speed modulation if the video signal is changed from the jitter signal to the non-jitter signal.